Understanding Oracle Application Express Architecture

Oracle Application Express installs with your Oracle database and is comprised of data in tables and PL/SQL code.

Whether you run the Oracle Application Express development environment or an application you built using Oracle Application Express, the process is the same. Your browser sends a URL request that is translated into the appropriate Oracle Application Express PL/SQL call. After the database processes the PL/SQL, the results are relayed back to your browser as HTML. This cycle happens each time you request or submit a page.

The application session state is managed in the database tables within Oracle Application Express. It does not use a dedicated database connection. Instead, each request is made through a separate database session, consuming minimal CPU resources.

About Oracle Application Express Listener, Oracle HTTP Server (Apache), and the Embedded PL/SQL Gateway

The version of Oracle Database you use determines how the URL is translated:

Versions prior to Oracle Database 11.1 require Oracle Application Express Listener or Oracle HTTP Server (Apache) with mod_plsql. The following graphic illustrates the three-tier architecture.

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With Oracle Database 11.1 or later or Oracle Database 10g Express Edition, you can use the embedded PL/SQL gateway. The following graphic illustrates the two-tier architecture using the embedded PL/SQL gateway.

Description of the illustration arch_epg.gif

The embedded PL/SQL gateway provides the Oracle database with a Web server and also the necessary infrastructure to create dynamic applications. The embedded PL/SQL gateway runs in the XML DB HTTP server in the Oracle database and includes the core features of mod_plsql. Inclusion of the embedded PL/SQL gateway simplifies the architecture and eliminates the middle tier entirely.